The present invention relates to a semiconductor integrated circuit and electronic equipment, and more particularly to a technology of power control of a semiconductor integrated circuit and electronic equipment made according to the cable connection status and the CPU operation status.
Interface standards such as IEEE (Institute of Electrical and Electronic Engineers) 1394 and HDMI (High-Definition Multimedia Interface) support “hot plugging” that permits insertion/removal of a cable during operation of equipment. Systems conforming to these interface standards are therefore provided with an insertion/removal detection circuit for detecting insertion/removal of a cable.
FIG. 6 shows a configuration of conventional IEEE 1394 interface equipment. Conventionally, a CPU 10, a link layer (LINK) 20 and a physical layer (PHY) 30 were implemented from individual chips. In recent years, however, semiconductor integrated circuits implementing the PHY 30 and the LINK 20 on one chip have come on the market.
An insertion/removal detection circuit 31 of the PHY 30 is kept powered so as to be able to detect connection of a cable C1 for a given peripheral equipment unit or a cable C2 for another peripheral equipment unit even when the PHY 30 is in a power-down mode. Once the insertion/removal detection circuit 31 detects an event of cable connection, it changes the logical level of a signal CDT. The CPU 10 then detects the cable connection from the change of the logical level, and performs recovery control for the PHY 30. Specifically, the CPU 10 instructs the PHY 30 to start operation by issuing a signal PWD. The PHY 30, which has started operation in response to this instruction, generates a clock signal CLK and supplies the generated clock signal to the LINK 20 that is in the power-down mode. With the supply of the clock signal CLK, the LINK 20 starts operation.
In the IEEE 1394 interface, power-down control can be made for the PHY 30 and the LINK 20 of which operation is unnecessary during no cable connection, to thereby attain power reduction. The CPU 10 however must continue operating for detecting the cable connection status. If the CPU 10 is also powered down, the recovery control of the PHY 30 will not be made even when the insertion/removal detection circuit 31 detects cable connection, and thus operation of relaying data transfer between the peripheral equipment (repeater operation) will not be available although the cables C1 and C2 are connected to the interface. In the IEEE 1394 interface, therefore, it is difficult to attain further reduction in power consumption as the entire interface equipment while enabling the function of the PHY 30 as the repeater.
There is another technique in which the recovery control of the PHY 30 that is in the power-down mode can be made when the insertion/removal detection circuit 31 detects cable connection, irrespective of the operation status of the CPU 10. According to this technique, the PHY 30 in the power-down mode recovers once the cables C1 and C2 are connected thereto even when the CPU 10 is in the power-down mode, and functions as the repeater.
In general, chattering occurs in insertion/removal of a cable, in which the cable connected and disconnected states are repeated alternately every interval of several milliseconds to several tens milliseconds. Therefore, chattering-caused noise is superimposed on a cable connection detection signal (signal CDT). Use of such a noise-containing cable connection detection signal for control of the interface equipment may cause a malfunction and thus is not desirable. It is therefore necessary to remove chattering-caused noise from the cable connection detection signal.
In the case described above that the PHY 30 is made to operate as the repeater when the CPU 10 is in the power-down state, since the clock signal CLK is supplied to the LINK 20 with the recovery of the PHY 30, the LINK 20 also recovers. However, as only the operation of the PHY 30 is required for the repeater operation, the LINK 20 should preferably be kept powered-down from the viewpoint of reduction in power consumption as the entire interface equipment.